1. Technical Field
The present invention relates to a light emitting device that can be used for lighting apparatus such as LED bulbs and spotlights.
2. Background Art
Generally, it has been known that light emitting devices using a light emitting element are compact and emit light of a clear color with good power efficiency. The light emitting elements according to the present invention are semiconductor elements, and are not prone to burn out, and in addition, have features such as excellent initial driving characteristics, durability to endure vibration, and repetitive ON/OFF operations. Due to such excellent properties, a light emitting device using a light emitting element such as a light emitting diode (LED) or a laser diode (LD) has been used as various light sources.
The light emitting device is mainly made of a light emitting element, a base member on which the light emitting element is disposed and has an electrically conductive wire which electrically connects the light emitting device with an external power source etc., and a sealing member covering the light emitting element on the base member. Also, there is a type in which a resin frame is formed around the light emitting element, as in a surface-mounting type COB (Chip on Board). Further, there is a light emitting device in which a fluorescent material is contained in a sealing member to obtain an emission of a mixed color light of light from the light emitting element and light whose wavelength has been converted by the fluorescent material.
In the light emitting device using fluorescent materials as described above, an absorption spectrum of a longer wavelength side (for example a CASN-based fluorescent material which emits a red light) partially overlaps with an emission spectrum of a shorter wavelength side (for example a YAG-based fluorescent material which emits a yellow light). Accordingly, a part of wavelength-converted light by the shorter wavelength side fluorescent material is absorbed by the longer wavelength side fluorescent material and decreases the light emitting efficiency, resulting in a decrease in the output power of the light emitting device. In order to improve the color rendering properties, a third fluorescent material (for example, a chlorosilicate which emits green light) which can compensate the absorbed wavelength is needed. However, inclusion of chlorosilicate leads the use of not only the blue light emission of the light emitting element (hereinafter may be called a blue light emitting element, and in a similar manner, for other colors, for example, a light emitting element which emits a blue-green light may be called a blue-green light emitting element) but also green light from a green fluorescent material for excitation of a fluorescent material which emits a red light (hereinafter may be called a red fluorescent material, and in a similar manner, for other colors, for example, a fluorescent material which emits yellow color may be called a yellow fluorescent material and a fluorescent material which emits green light may be called a green fluorescent material), which may result in a decrease in the light emitting efficiency.
For this reason, a light emitting device has been proposed in which two kinds of fluorescent material regions (regions containing fluorescent materials respectively) are separated (for example, see Patent Literature 1). In the light emitting device described in Patent Literature 1, a green sealing resin containing a green fluorescent material and sealing a first blue light emitting element and a red sealing resin containing a red fluorescent material and sealing a second blue light emitting element are separated by a dividing wall.
For example, the light emitting devices according to Patent Literature 2 and Non-patent Literature 1 respectively include two fluorescent material regions of an incandescent lamp color region which is an inner side region and a white color region which is an outer side region. The incandescent lamp color region of the inner side contains a mixture of a red fluorescent material and a yellow fluorescent material, and the white color region of the outer side contains a yellow fluorescent material. In the light emitting device, the electric current supplied to the incandescent light color region and the white color region are separately controlled to adjust the proportions of intensities of light of the two regions so as to adjust the color temperature.
Patent Literature 3 describes a light emitting device in which a region surrounded with a resin frame is divided in a rectangular shape by a resin dividing wall.